To process radar signals, for example within vehicles, several radar devices may cooperate to determine and process a radar signal reflected from a target. Increasing the number of radar devices which cooperate to process a reflected radar signal may increase the spatial resolution of the system, for example an azimuthal and elevational resolution with which the target is determined relative to the radar devices. A single radar device of, for example, an automotive radar system, typically comprises a transmit chain to generate the radar signal to be sent and a receive chain to receive and process the reflected radar signal. The transmit chain comprises an oscillator circuit to generate the radar signal and a power amplifier to amplify the radar signal. Typical frequencies of local oscillator signals may, for example, be 38 GHz and 77 Ghz. The power amplifier is coupled to one or more transmit antennas which radiate the radar signal into the environment. The reflected radar signal is received by an array of receive antennas operating as a phased array. The reflected radar signal received by a single antenna is amplified by a low noise amplifier before being further processed. In a continuous wave radar device, the oscillator circuit generates a local oscillator signal which exhibits a time varying frequency, for example increasing or decreasing linearly in a ramp like manner. The oscillator signal is used to generate the radar signal to be sent as well as to downmix the received radar signal into a downconverted radar signal using a mixer circuit. A downconverted radar signal may also be referred to as a baseband signal.
The frequency of the downconverted radar signal so correlates to the time difference between sending and receiving the radar signal and, hence, to the distance of a reflecting object. Within the radar device, the downconverted radar signal of each antenna is typically digitized by means of an analog to digital converter (ADC) and the digitized downconverted radar signals are further processed to, for example, combine the downconverted radar signals of all receive antennas to determine an azimuth and an elevation estimate for each reflecting target within a field of view of the radar device. The location may so be determined relative to the radar device and, for example, given by two angles (elevation and azimuth) and a distance. In order to operate as a phased array, downmixing and sampling of the radar signals received by all antennas of the array of an individual radar device is performed synchronously.
In order to enable cooperative processing of several radar devices, it may be required to also synchronize the processing of the signals received by means of the antennas of the different radar devices. In particular, it may be of importance to sample the signal received by all antennas of the cooperating radar devices at the same time instant in order to, for example, determine the location of a radar reflecting target without an error.
In order to achieve such synchronicity, a sampling clock signal can be distributed synchronously to all the analog to digital converters of the cooperating radar devices to define the time instants at which each analog-to-digital converter samples the signal of the antennas in an individual radar device. In order to guarantee synchronous arrival of the sampling clock signal at each radar device and its analog-to-digital converters in such an approach, high effort may be required in, for example, routing the sampling clock signal between a generator of the sampling clock signal and each individual radar device so that no propagation time differences occur on the different routes to the individual cooperating radar devices. Routing constraints might also limit the flexibility in setting up a radar system in that it may be infeasible to extend the number of cooperating radar devices on a given printed circuit board if no more space for appropriate routing is available.